Smart battery charger system

ABSTRACT

A smart battery charger system including a smart battery charger that responds to charging instructions of a smart battery. The smart battery includes a memory that stores battery-specific charging characteristics. The smart battery determines a desired charging voltage and desired charging current based on measured environmental conditions, such as battery temperature, and the charging characteristics. A bus allows the smart battery to communicate the desired charging voltage and charging current to the smart battery charger. The smart battery charger generates the actual charging voltage and charging current in response to the desired charging voltage and charging current. In this manner the smart battery can control its own charging. Charging can be optimized according to a particular smart battery&#39;s charging characteristics and requirements.

RELATED APPLICATIONS

This patent application is related to the following patent applicationswhich are assigned to the assignee of the present invention and filedconcurrently herewith: patent application Ser. No. 08/357,412, entitled"Smart Battery, Providing Programmable Remaining Capacity And Run-TimeAlarms Based On Battery-Specific Characteristics," patent applicationSer. No. 08/356,906, entitled "Smart Battery Power Availability FeatureBased On Battery-Specific Characteristics," and patent application Ser.No. 08/356,905, entitled "Smart Battery Providing Battery Life AndRecharge Time Prediction."

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to battery chargers, and morespecifically to a smart battery charger system wherein a smart batterycharger responds to charging instructions supplied by a smart battery.

2. Related Art

Rechargeable batteries are used in many of today's portable electronicdevices, such as computers, camcorders, and cellular phones. Typically,these electronic devices are also capable of utilizing AC power. Batterypower is utilized when AC power is not convenient or is not available.

It is often important to provide accurate information regarding theremaining capacity of the battery. Some batteries provide a "fuel gauge"that gives an indication of the charge level of the battery. Forexample, U.S. Pat. No. 5,315,228 (the '228 patent) describes arechargeable battery that measures battery discharge current andestimates battery self-discharge to predict the remaining capacity ofthe battery (i.e., how full the "tank" is to continue the analogy of the"fuel gauge"). Self-discharge refers to a loss battery capacity thatoccurs even when the battery is not supplying any discharge current to aload. The '228 patent describes self-discharge as being estimated fromexperimental observations of battery self-discharge. For example, in the'228 patent a fully charged Ni-MH (nickel metal hydride) battery isestimated to self-discharge at a rate of approximately 6% the first 6hours and a Ni-Cd (nickel cadmium) battery is estimated toself-discharge at a rate of 3% the first six hours. Both batteries areestimated to self discharge at rates of about 1.5% the second six hourperiod, about 0.78% the third and fourth six hour periods, andapproximately 0.39% for each subsequent six hour period. For partiallydischarged batteries, self-discharge is estimated to be about 0.39% foreach six hour period. (See column 12, line 59--column 14, line 4.)

However, this approach for predicting battery capacity does not accountfor the dependence of self-discharge or battery capacity onenvironmental conditions, such as battery temperature. FIGS. 1A and 1Billustrate typical self-discharge characteristics as a function oftemperature for rechargeable batteries. In certain situations, the '228patent's method for estimating self-discharge can produce unacceptableerrors in the "fuel gauge" remaining capacity indication. Under hightemperature conditions, the self-discharge can be much greater than theestimated values. For example, one scenario could include a videocamcorder and battery being stored in a car on a series of hot, sunnydays, causing the battery's "fuel gauge" to erroneously indicate morethan enough charge to film a 20-minute wedding ceremony. The scenarioconcludes with an irate father when his camcorder shuts off 10 minutesinto the ceremony, without a spare battery.

To provide warning of low battery conditions, some computer systemsprovide a run-time alarm that indicates when the battery has less than afixed amount of time remaining at the present discharge rate. In otherwords, the alarm is triggered if:

(estimated battery capacity/present discharge rate)<fixed alarm time.The above-described "fuel gauge" is used to indicate battery capacityfor this run-time alarm. This type of run-time alarm has severaldrawbacks in computer systems. First, the present discharge rate doesnot adequately reflect the dynamic discharge rates in the computer. Forexample, in today's laptop and notebook computers, power consumptionvaries dynamically, on the order of several hundred milliamps (mA). Thisvariation is due to power management systems that turn on and off thehard-disk, LCD screen backlight, CPU, etc., under various conditions tosave power. Second, the battery capacity provided by the above "fuelgauge" is inaccurate because the dependence of self-discharge onenvironmental factors, such as temperature, humidity, air pressure, isnot considered. Third, the alarm value is fixed. This removesflexibility from the power management system for adjusting the alarmvalue to the varying power conditions in the system.

Another drawback of today's rechargeable batteries is they do notprovide the systems they power with an indication of whether there isenough power remaining to perform a given task, i.e., the poweravailability of the battery. Although the above "fuel gauge" providessome indication of a battery's remaining capacity, it does not providespecific information about whether the battery can provide a specifiedamount of additional power to perform a task. For example, near totaldischarge, a laptop computer may need to know whether there issufficient battery power available to spin-up the hard disk to save afile before saving the state of the machine and powering down. What thecomputer needs to know is whether the battery is capable of providingthe power for the additional task without the battery's terminal voltagedropping below a cut-off value.

Yet another drawback of today's rechargeable batteries is that they donot provide an accurate indication of remaining battery life based on auser-specified discharge rate. The prior "fuel gauge" gives an estimateof the amount of remaining charge in the battery based on the presentdischarge rate, but provides no indication regarding how long thebattery will continue to provide power at other discharge rates. Thebattery does not tell the user, and the user cannot ask the battery, howlong the battery will continue to supply power if the discharge rate isvaried. In addition, neither the above "fuel gauge" nor run-time alarmaccount for the effect of environmental conditions or large batteryloads on battery capacity.

Charging is another key aspect of rechargeable batteries. Variousmethods for charging batteries are known, such as quick charging andtrickle charging. With respect to recharge time, the general goal is tocharge the battery as quickly as possible without damaging the battery.Charging may cause the battery to heat up. Overheating during chargingmay damage the battery. For some batteries, such as Ni-Cd, one way ofavoiding battery damage during charging is to monitor batterytemperature and switch from quick charging to trickle charging if thetemperature exceeds a safe level. Such efforts can prevent damage to thebattery, but do not necessarily optimize the charging of the battery.For example, minimizing charge time while avoiding destructiveconditions may optimize recharge time at the expense of reducing thetotal number of charge/discharge cycles the battery can provide. Thus,the overall useful life of the battery would be reduced.

Typical battery chargers are designed for use with a specific type ofbattery. For example, a charger may be designed specifically forcharging Ni-Cd batteries, which are charged with a specific constantcurrent, voltage limit, and end-of-charge criteria. However, ongoingimprovements to Ni-Cd batteries, such as changes in battery chemistry orcell design, may require that newer Ni-Cd batteries be optimally chargedat a different constant current and/or different voltage limit, notprovided by the original charger. In addition, charging conditions varywith battery type. For example Ni-MH and Ni-Cd batteries are typicallycharged at a constant current with a voltage limit. Some lithium-ion andlead-acid batteries are charged at a constant voltage with a currentlimit. Today's battery chargers are not capable of dynamically adaptingto meet the various charging needs of different types of batteries,different battery chemistries, and different battery cell designs. Norare today's battery chargers capable of adapting to meet changingcharging needs as battery chemistries and cell designs change over time.

Another drawback of present battery charging techniques is that noaccurate indication is provided as to how long it will take to fullycharge the battery from its present capacity. For example, it would beadvantageous to know how long it will take to charge a battery that ispresently at half capacity.

In summary, rechargeable batteries, such as those used in today'selectronic equipment such as laptop computer systems, cellulartelephones and video cameras, presently pose a number of problems fromboth the user's and the equipment's perspective. First, they representan unpredictable source of power. Typically a user has little advanceknowledge that their battery is about to run out or how much operatingtime is left. Second, equipment powered by the battery can not determineif the battery, in its present state, is capable of supplying adequatepower for an additional load (such as spinning tap a hard disk). Third,battery chargers must be individually tailored for use with a specificbattery chemistry and cell design and may cause damage if used onanother battery with a different chemistry or cell design.

Therefore, a smart battery charger system wherein a smart batterycharger responds to charging instructions of a smart battery is needed.

SUMMARY OF THE INVENTION

The present invention covers a method and apparatus for a smart batterycharger system. The system includes a smart battery charger thatresponds to charging instructions of a smart battery. The smart batterygenerates the charging instructions based on battery-specific chargingcharacteristics and the environmental conditions of the battery. In thismanner, a smart battery can optimize various charging features accordingto the particular charging characteristics and charging requirements ofthe battery.

In one embodiment, the smart battery charger includes a charging unit, alogic unit, and a memory. The memory stores a charging current value anda charging voltage value. The logic unit programs the charging currentvalue in response to a set current value command and the chargingvoltage value in response to a set voltage value command. The chargingunit generates a charging current and a charging voltage according tothe charging current value and the charging voltage value, respectively.

One embodiment of a smart battery charger system includes a smartbattery and a smart battery charger. The smart battery includes a memoryand a logic unit. The memory stores one or more charging characteristicsof the smart battery. The logic unit determines a desired chargingcurrent and a desired charging voltage according to one or moreenvironmental conditions of the battery and the charging characteristicsof the battery. The smart battery charger generates an actual chargingcurrent and an actual charging voltage in response to the desiredcharging current and the desired charging voltage, respectively,determined by the logic unit of the smart battery.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements.

FIG. 1A illustrates an exemplary self-discharge current characteristicas a function of temperature for a rechargeable battery.

FIG. 1B illustrates another exemplary self-discharge characteristic fora specific battery chemistry showing retained charge as a function oftime for various temperatures.

FIG. 2 is a block diagram of one embodiment of a smart battery system.

FIG. 3 is a block diagram of another embodiment of a smart batterysystem.

FIG. 4 is a block diagram of one embodiment of a smart battery.

FIG. 5A is a graph, for a particular cell design and chemistry, ofbattery cell voltage as a function of discharge rate for various loadcurrents. FIG. 5A illustrates that battery capacity may be dependent ondischarge rate.

FIG. 5B is a graph, for a particular cell design and chemistry, of abattery's capacity as a function of temperature for various loadcurrents.

FIG. 6 is a flowchart of the present invention method for a programmableremaining capacity alarm and programmable remaining run-time alarm.

FIG. 7 is a flowchart of the present invention method for indicatingwhether a battery can provide a desired additional amount of power.

FIG. 8 is a flowchart of the present invention method for predicting theremaining life of a battery based on a user-defined discharge rate.

FIG. 9 is a block diagram of a smart battery system using one or moresmart batteries.

FIG. 10 is a block diagram of a smart battery charger.

FIG. 11A is a graph illustrating the -dV/dt (voltage decrease) atend-of-charge for particular Ni-Cd and Ni-MH batteries.

FIG. 11B is a graph illustrating a particular battery's chargingcharacteristic for different temperatures.

FIG. 11C is a graph illustrating a particular battery's chargingcharacteristics for different charging currents.

FIG. 12 is a flowchart illustrating the present invention method forpredicting the recharge time of a battery.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

A method and apparatus for a smart battery charger system including asmart battery charger that responds to charging instructions of a smartbattery is described. In the following description, numerous specificdetails such as currents, voltages, temperatures, power, and batterycharacteristics are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-known methodsand circuits are shown in block diagram form in order not to obscure thepresent invention.

FIG. 2 is a block diagram of one embodiment of a smart battery system ofthe present invention. A system host 20, a smart battery charger 22, asmart battery 24, and other SMBus devices 26 are coupled to a SystemManagement Bus (SMBus) 28. SMBus 28 provides communication and signalingbetween the devices coupled to it. Smart battery 24 can provide systemhost 20 and smart battery charger 22 with present capacity and charginginformation. System host 20 gets and reports to the user informationsuch as remaining battery capacity, how much battery operating time isleft, and whether the battery can provide adequate power for anadditional load. In addition, the system provides for optimal chargingof smart battery 24. SMBus devices 26 represent other smart electronicdevices that communicate over SMBus 28. For example, the back-lightcontroller in a notebook computer can be implemented as smart device andcontrolled by the system's power management scheme.

FIG. 3 is a block diagram of another embodiment of a smart batterysystem 44 of the present invention. A System Management Bus (SMBus) 38provides communication and signaling between devices according to adefined protocol. In one embodiment, the protocol of the SMBus 38 isbased on the I² C-bus protocol, developed by Philips. I² C is a two-wirebus protocol designed tier data transport between low-speed devices. Asystem host 30, a smart battery charger 32, and a removable smartbattery 34 are coupled to the SMBus 38.

Smart battery 34 is a rechargeable battery that is equipped withelectronics to provide present capacity and charging information aboutthe battery to system host 30 and smart battery charger 32. Theelectronics can be embedded in the battery pack, or exist outside thebattery pack. Wherever located, the electronics must be able to measurethe environmental conditions of the smart battery 34. Smart battery 34maintains information regarding its environment, chargingcharacteristics, discharge characteristics, self-dischargecharacteristics, capacity characteristics, present capacity, and totalcapacity. This battery-specific information may be stored with, orseparate from, smart battery 34, but must be battery-specific. Typicallythe battery-specific information is maintained within smart battery 34.The characteristics stored may be functions of temperature, batterycurrent, battery voltage, environmental conditions, or other variablesaffecting battery performance. The battery characteristics may be storedin the form of tables, formulas, or algorithms that represent thecharacteristics of the battery. Environmental information tracked bysmart battery 34 may include battery temperature, humidity, airpressure, or other conditions that influence battery performance and/orcapacity. Smart battery 34 may also include programmable alarm valuesfor events, such as over-charge, over-voltage, over-temperature,temperature increasing too rapidly, remaining run-time and remainingcapacity.

Based on the battery-specific characteristics, measured environmentalconditions, measured battery current, and battery history (batterycapacity can be affected by the charge/discharge history of thebattery), smart battery 34 can accurately determine present batterycapacity. Based on the present battery capacity, smart battery 34 canpredict remaining battery run-time based on either the present dischargerate or a user-supplied discharge rate. Similarly, smart battery 34 candetermine whether an amount of power can be supplied. The amount ofpower can either be a total amount of power or an amount of power inaddition to that already being supplied by the smart battery 34.Similarly, smart battery 34 can also determine its optimal chargingvoltage and charging current. In summary, based on battery-specificcharacteristics, measured battery conditions, and present batterycapacity, smart battery 34 can accurately determine remaining batterylife, power availability, and optimal charging conditions. Smart battery34 can provide this information to the system host 30 and the smartbattery charger 32 to provide users with usefull battery information,improve system power management, optimize battery charging, and maximizebattery life.

It is advantageous that smart battery 34 maintain its own informationbecause batteries, each being unique, are frequently changed in asystem. A good example is a video camcorder where a user may havemultiple batteries each with different design capacities, chemistries,and charge states. Even with an accurate state-of-charge indication, afull one AH (ampere hour) battery is not equivalent to a full 1.5 AHbattery. Though they both can power the same camcorder, what the userwrests to know is whether or not either of these batteries has adequatecapacity to record a one-hour event. Smart battery 34 provides the userwith accurate remaining capacity information along with an accurateprediction of the remaining operating time.

Another advantage is that smart battery 34 provides information forpower management and charge control regardless of the particularbattery's chemistry or construction. System host 30 can use thebattery-specific power information to better manage the powerconsumption of the system. Smart battery charger 32 can use thebattery-specific charging information to optimize the charging of smartbattery 34.

System host 30 is a piece of electronic equipment powered by smartbattery 34. For example, system host 30 could be a notebook computer,video camera, or cellular phone. System host 30 can communicate withsmart battery 34 via SMBus 38 to request information from smart battery34. System host 30 then uses the battery information in the system'spower management scheme and/or uses it to provide the user withinformation about the smart battery's 34 present state and capabilities.System host 30 also receives critical events from smart battery 34 whensmart battery 34 detects a problem. These critical events may includecapacity alarm and run-time alarm signals sent to the system host 30.They may also include alarms sent to smart battery charger 32.

Smart battery charger 32 is a battery charger that periodicallycommunicates with smart battery 34 and alters its charging outputs (suchas charging voltage and/or current) in response to information providedby smart battery 34. Smart battery charger 32 may be implemented atvarious levels. A level 1 smart battery charger 32 provides fixedcharging outputs that are altered in response to critical alarm messagesfrom the smart battery 34. A level 2 smart battery charger 32 alters thecharging voltage and/or charging current in response to charginginstructions from smart battery 34 and also responds to critical alarmmessages. A level 3 smart battery charger 32 periodically polls smartbattery 34 for charging information and may adjust its charging outputsaccordingly. A level 3 smart battery charger 32 may also ignore thebattery's charging requests and use its own charging algorithm, such asa specific charging pattern. Level 3 smart battery chargers may alsorespond to critical alarm messages. Level 1, 2, and 3 smart batterychargers are described further below. In summary, smart battery charger32 periodically receives information from smart battery 34 indicatinghow smart battery 34 would like to be charged. Smart battery 34determines optimal charging conditions based on the smart battery's 34charging characteristics, present charge level, and environmentalconditions. Smart battery charger 32 may adjust its charging voltageand/or charging current in response to the desired charging voltage anddesired charging current information received from the smart battery 34.

Thus, smart battery 34 can control its own charge cycle to optimizecharge time, prolong battery life, and prevent destructive chargingconditions. Charging time can be optimized by adjusting chargingaccording to the smart battery's 34 specific charging characteristics.The life of smart battery 34 can be prolonged by avoiding chargingconditions that shorten battery life. For example, repeated shortdischarge/charge cycles or overcharging can shorten battery life. Smartbattery 34 may determine that charging is not desirable if presentcharge capacity is, for example, already above 85%. Smart batterycharger 32 can avoid destructive charging conditions by stopping oraltering charging when smart battery 34 detects critical events such as:over-charge, over-voltage, over-temperature or temperature increasingtoo rapidly.

AC-DC converter 36 converts AC power received from AC plug 42 to DCpower. System power supply 40 receives DC power from either smartbattery 34 or AC-DC converter 36 and generates a variety of DC voltagesfor system host 30. Vbatt represents the battery voltage providedbetween the POSitive and NEGative battery terminals. Many electronicsystems require voltages of V_(CC) (typically 5.0 and/or 3.3 volts), +12volts, and -12 volts. The thermistor is a temperature sensor for sensingbattery temperature. The temperature sensor may also be used to providean independent safety mechanism and/or to signal a "default" chargingalgorithm.

The communication events that can occur within the smart battery system44 can be divided into several types, including but not limited to: 1)system host 30 to smart battery 34, 2) smart battery 34 to system host30, 3) smart battery 34 to smart battery charger 32, 4) smart batterycharger 32 to smart battery 34, and 5) system host 30 to smart battercharger 32.

Communication between system host 30 and smart battery 34 can be used toget data for either a user or the system host's 30 power managementsystem. The user can get three types of data from the battery:characteristic data, measured data, and calculated data. Characteristicdata includes battery characteristics, such as pack design voltage, packdesign capacity, and charging and capacity characteristics as a functionof the battery's environmental conditions. Measured data is data that ismeasured, such as battery temperature. Calculated data is data that isdetermined based on characteristic data and measured data. For example,self-discharge data is determined based on measured environmentalconditions and a battery's self-discharge characteristics. Additionally,since the smart battery 34 has a clock, timer, or other means fortracking time, the information can be presented as a rolling averageover a fixed interval. The clock also allows the battery to periodicallytrack its environment over time.

The system host's 30 power management system may query a device driverto determine if an action will cause harm to the system's integrity. Forexample, spinning up a disk drive at the end of the battery's chargemight cause its output voltage to drop below acceptable limits thuscausing a system failure. In order to prevent this, the device driverneeds information from the battery that will allow it to do the rightthing. If the driver queries the battery and discovers that not enoughpower is available, the driver can request that the power managementsystem turn off a non-critical power use such as the LCD screenback-light and then try again. The driver could also disallow the actionand/or request that the user plug in AC power.

In summary, communication between system host 30 and smart battery 34may be performed: to allow the user to know the smart battery's 34remaining life; to tell the user how long it will take to charge smartbattery 34; to allow smart battery 34 to provide accurate batteryinformation to the user; to determine the system host's 30 real-timepower requirements; to enable power management based on "real"information supplied by the battery; to enable battery manufacturers tocollect information about a smart battery's 34 usage; and to allowbattery manufacturers to electronically "stamp" batteries at time ofmanufacture.

Communication between smart battery charger 32 and smart battery 34 canbe performed: to allow smart battery 34 to be charged as rapidly and assafely as possible, to allow new and different battery chemistries andcell constructions to be used, to allow access to the "correct" chargingalgorithm for the battery, and to allow smart battery 34 to be chargedin a way that maximizes the life of smart battery 34.

Communication between smart battery 34 and smart battery charger 32and/or system host 30 can be performed: to allow smart battery 34 towarn other system components of potential problems, to allow smartbattery 34 to warn the user, power management system, or smart batterycharger about potentially dangerous situations that the user canrectify, and to allow smart battery 34 to instruct the smart batterycharger what charge current and charge voltage to generate.

FIG. 4 is a block diagram of one embodiment of the smart battery of thepresent invention. Smart battery 82 includes rechargeable battery 80 andother electronic circuitry. The electronic circuitry may or may not bephysically embedded in the same battery pack as rechargeable battery 80.Wherever located, the electronic circuitry must be able to measure theenvironmental conditions of the smart battery 82 and contain, or store,the battery-specific characteristics of that smart battery (i.e., thestored battery characteristics must be battery-specific). Rechargeablebattery 80 provides the electrical power of smart battery 82.Rechargeable battery 80 may include one or more battery cells that areconnected in either a series, parallel, or series/parallel combinationto form a battery pack. For example, ten battery cells, each having acell voltage of 1.2 volts, can be connected in series such thatrechargeable battery 80 provides a voltage of 12.0 volts. POS 50 and NEG52 are the positive and negative power terminals, respectively, of smartbattery 82 that together provide the voltage V_(BATT) 51. DATA 54 andCLOCK 55 are data and clock terminals, respectively, that provide acommunication interface to the DATA and CLOCK lines, respectively, ofSMBus 53. Other communication interfaces, such as a single-wireinterface, may also be used with the smart battery.

Microcontroller 56 includes a logic unit 58, a non-volatile memory 60, aclock 59, and an analog-to-digital (A/D) converter 72. Logic unit 58 maybe a CPU, processor, or random logic that performs the smart batteryfunctions. Non-volatile memory 60 may comprise flash, ROM, EPROM,EEPROM, and other types of non-volatile memory (non-volatile meaning itretains stored values even in the absence of electrical power). Volatilememory, such as SRAM or DRAM memory, may also be used in otherembodiments. Non-volatile memory 60 stores a capacity alarm value 61, arun-time alarm value 62, a present run-time value 63, a present capacityvalue 64, one or more self-discharge characteristics 65, one or morecharging characteristics 66, one or more discharge characteristics 67,one or more capacity characteristics 68, mode and status bits 69, auser-specified discharge rate 70, and a user-specified charge rate 71.In one embodiment, battery characteristics 65-68 are stored in a ROMmemory while alarm values 61-62, run-time and capacity values 63-64,mode and status bits 69, user-specified discharge rate 70, anduser-specified charge rate 71 are stored in a non-volatile memory thatis both readable and writeable, such as flash or EEPROM memory.Microcontroller 56 may also include RAM memory. Characteristics 65-68may be stored in the form of tables of data, formulas, or algorithms,representing the various battery characteristics. Clock 59 is a digitaltimer, counter, or clock that provides logic unit 58 with elapsed timeinformation. Clock 59 can also generate interrupts to cause logic unit58 to perform actions, such as periodically updating the presentcapacity value 64. A/D converter 72 converts analog signals produced bya current measurement circuit 74, a voltage measurement circuit 76, andan environment monitoring circuit 78 into digital form for use by logicunit 58.

Current measurement circuit 74 measures the actual current (charge ordischarge) of rechargeable battery 80. Current measurement circuit 74 toreceives a voltage, V_(sense), developed across a small resistor (e.g.,0.01 Ω) that is coupled between the NEG 52 battery terminal andrechargeable battery 80. The V_(sense) voltage is directly proportionalto a current I_(sense), which is the actual charge/discharge current ofthe smart battery 82. The current measurement circuit 74 generates ananalog output voltage proportional to the measured charge/dischargecurrent. Current measurement circuit 74 provides appropriate scaling ofthe voltage input to A/D converter 72. Circuits for measuring currentare well-known in the art. Voltage measurement circuit 76 measures theactual terminal voltage of rechargeable battery 80 and produces ananalog output proportional to the measured terminal voltage. Voltagemeasurement circuit 76 provides appropriate scaling of the terminalvoltage for input to A/D converter 72. Environment monitoring circuit 78measures the environmental conditions of smart battery 82, such asbattery temperature, humidity, altitude, or other conditions affectingbattery characteristics. Environment monitoring circuit 78 may include atemperature sensor, such as a thermistor, a thermocouple, asemiconductor temperature sensor, or other temperature sensing device,that produces an analog signal proportional to the sensed temperature.Again, appropriate amplifier/offset circuitry for scaling the analogsignal for input to A/D converter 68 is provided. Environment monitoringcircuit may sense conditions of the battery cells of rechargeablebattery 80 or conditions of the smart battery 82 (i.e., the batterypack).

Logic unit 58 receives the smart battery's 82 current, voltage, andbattery environment information from A/D converter 72 and the batterycharacteristics from non-volatile memory 60. Based on this information,the logic unit 58 can determine present battery capacity, poweravailability, predicted run-time, predicted recharge time, and optimalcharging conditions.

FIG. 5A is a graph of battery cell voltage as a function of dischargecapacity for load currents of 3 C, 1 C, and 0.2 C for a particularbattery. The graph illustrates that a higher discharge current reducesthe cell voltage. The graph also shows that higher discharge currentreduces the capacity of the battery. This is one of the batterycharacteristics that may be stored in nonvolatile memory 60 of FIG. 4.Note that C is a unit indicating battery capacity. By convention,battery capacity is interpreted at a C/5 discharge rate. For example, abattery having a capacity of 2 AH (C) means the battery can provide acurrent of 400 mA for 5 hours (2 ampere-hours/5 hours).

FIG. 5B is a graph of a particular battery's discharge capacity as afunction of temperature for discharge currents of 0.3 C and 1 C. Thisbattery characteristic illustrates the dependency of battery capacity ontemperature and load current.

FIG. 6 is a flowchart of a method for a programmable remaining capacityalarm and programmable remaining run-time alarm based onbattery-specific characteristics. At step 90, the capacity alarm valueand run-time alarm value are set to specified values by the user, thepower management system, or by other means. For example, a user mayprogram the capacity alarm value to trigger the remaining capacity alarmwhen the battery has 10% remaining capacity and program the run-timealarm value to trigger the remaining run-time alarm when the battery ispredicted to have a remaining life of 5 minutes. In one embodiment, thealarms are set by writing data to certain locations in the smartbattery's memory. In a smart battery system such as that of FIG. 3, thesystem host can set the alarms of the smart battery via the SMBus.

At step 92, a remaining capacity value of the battery is periodicallyupdated by: 1) measuring the battery's environmental conditions, such asbattery temperature, 2) measuring actual battery current, 3) determiningan incremental self-discharge of the battery (the incrementalself-discharge is determined from one or more of the battery'scharacteristics and the measured environmental conditions of thebattery, and 4) changing the remaining capacity value by the incrementalself-discharge and the measured battery current. In one embodiment, theincremental self-discharge is based on the battery's self-dischargecharacteristic and the measured temperature of the battery. In addition,the battery's capacity characteristic can be taken into account whenupdating the remaining capacity value. The battery's capacitycharacteristic is an indicator of how the battery's capacity changeswith temperature and/or other battery conditions. In particular, thebattery's capacity characteristics may be functions of environmentalconditions and/or the battery current. The remaining capacity value isan accurate indication of the remaining capacity of the battery.

At step 93, the method periodically updates a remaining run-time valuebased on the remaining capacity value and the present discharge rate ofthe battery. Thus, the remaining run-time value is a prediction of theremaining battery life based on the present battery capacity, assumingthat the present discharge rate remains constant.

During step 94, the method determines whether the remaining capacityvalue is less than the capacity alarm value. If so, the method proceedsto step 96 where the smart battery sends a capacity alarm signal to thesystem host, warning of low battery capacity. If not, the methodproceeds to step 95.

At step 95, the method determines whether the remaining run-time valueis less than the run-time alarm value. If so, the method proceeds tostep 97 where the smart battery sends a run-time alarm signal to thesystem host. If not, the method returns to step 92 to again update theremaining capacity value.

After either step 96 (sending a capacity alarm signal) or step 97(sending a run-time alarm signal), the method jumps back to step 92 toupdate the remaining capacity value again.

FIG. 7 illustrates a flowchart for the present invention method fordetermining whether a battery can supply a desired amount of power. Atstep 98, a desired amount of power is selected. Alternatively, an amountof power in addition to that presently provided may be selected (i.e., adesired amount of additional power). At step 100, the system hostqueries the battery whether the battery can supply the desired mount ofpower. At step 102, the battery determines whether it can supply thedesired amount of power by: 1) measuring the environmental conditions ofthe battery, 2) determining the present battery capacity, preferably bythe method shown in FIG. 6, 3) measuring the present discharge rate ofthe battery, and 4) determining whether the battery can supply thedesired amount of power according to the measured conditions, presentbattery capacity, present discharge rate, and one or morecharacteristics of the battery. For example, the characteristic of FIG.5A illustrates the effect of changing the discharge current on thebattery capacity. The characteristic of FIG. 5B shows the effect oftemperature and battery current on battery capacity.

At step 104, the battery indicates to the system host whether, or not,the battery can supply the desired amount of power.

FIG. 8 is a flowchart illustrating the present invention method forpredicting the remaining life of a battery based on a selected dischargerate. For example, the power management system in a computer may providethe following options to a user:

    ______________________________________                                        User Selects   Expected System Discharge Rate                                 ______________________________________                                        High Performance                                                                             1000 mA                                                        Medium Performance                                                                            700 mA                                                        Conserve Power  300 mA                                                        Select a Rate  <enter rate>                                                   ______________________________________                                    

These represent user-selectable performance/power options available tothe user. However, what the user may really be interested in is whetherthe battery will survive his two hour airline flight. The indicateddischarge rates for the various performance levels may be determined bya power management system such that they are a reasonably accurateindication of actual discharge. If the user selects the "HighPerformance" option the present invention battery life prediction methodmay predict a predicted battery life of 90 minutes. Selecting the"Medium Performance" option may predict a battery life of 2 hours and 5minutes. Selecting the "Conserve Power" option may indicate a predictedbattery life of 5 hours. If the "Select a Rate" option is selected, theuser can enter a custom discharge rate and the power management systemwill attempt to manage the system's power consumption accordingly. Thus,predicted battery life based on user-defined discharge rates allows theuser to determine which performance/power option best matches hispresent needs.

Turning to the present invention battery life prediction method, at step110 a discharge rate is selected. The discharge rate may be selected bya user, a power management system, or by other means. The system hostqueries the battery for the estimated remaining life of the battery atthe selected discharge rate.

At step 112, the method determines the predicted life of the batteryby: 1) measuring the battery's environmental conditions, such as batterytemperature, 2) determining present battery capacity, preferably by themethod of FIG. 6, and 3) determining the predicted remaining life of thebattery based on the measured battery conditions, the present batterycapacity, the selected discharge rate, and one or more characteristicsof the battery. For example, the characteristics of FIG. 5A and FIG. 5Bmay be used.

At step 114, the battery returns the predicted remaining life of thebattery to the system host via the SMBus.

FIG. 9 illustrates a smart battery system that includes two smartbatteries, smart battery #1 124 and smart battery #2 125. A smartbattery selector 127 connects the smart batteries to either smartbattery charger 122, system host 120, or disconnects them, asappropriate. Smart battery #1 124 is powering the system. Smart battery#2 125 is being charged by the smart battery charger 122.

FIG. 10 is a block diagram of one embodiment of a smart battery chargerof the present invention. A smart battery charger 162 includes DATA 154and CLOCK 156 terminals that allow communication with other componentsof a smart battery system via the DATA and CLOCK lines of the SMBus 153.A logic unit 158 performs the communication functions of the smartbattery charger 162. A charging unit 160 generates a charging voltageand a charging current at POSitive 150 and NEGative 152 terminals of thesmart battery charger 162 in response to a charging current value 164and a charging voltage value 166 stored in the smart battery charger162. The charging current value 164 and/or the charging voltage value166 may be limits, rather than absolute values. The POS 150 and NEG 152terminals are connected to the corresponding terminals of the smartbattery being charged. The charging current value 164 and chargingvoltage value 166 are programmable by other SMBus devices of the systemvia the SMBus 153. In other words, logic unit 158 programs the valuesaccording to commands received via the SMBus 153. In one embodiment,charging unit 160 is not required to output precisely the chargingcurrent and charging voltage indicated by the charging current value 164and charging voltage value 166, respectively. In this embodiment, thesmart battery is responsible for precisely controlling the chargingcurrent and charging voltage. However, for reliable operation thecharging unit 160 should respond monotonically (i.e., eitherconsistently increase or decrease but do not oscillate in relativevalue) to increases or decreases in the charging values. In anotherembodiment, the charging unit 160 includes sensors and feedbackcircuitry to output precisely the charging current and charging voltageindicated by the charging current value 164 and charging voltage value166, respectively.

Refer now to FIG. 3 to further discuss the operation of a smart batterycharger in a smart battery system. The electrical characteristics ofsmart battery charger 32 feature charging characteristics that arecontrolled by the smart battery itself, in contrast to a charger withfixed charging characteristics that is designed to charge only oneparticular cell type. The smart battery and smart battery chargercombination provide two distinct advantages in system performance andcost. First, charging characteristics are integral to the batteryitself, allowing for ideal charging algorithms that match the specificcell types. Each smart battery defines the charging scheme that is bestsuited to its chemistry, cell construction and capacity. Charging can betailored to maximize the usable energy at each charge, reduce the chargetime, and/or maximize the number of charge cycles. Second, the cost andcomplexity of the system can be reduced as the charger need only providethe charging voltage and current specified by the Smart Battery, withoutduplicating the measurement and control electronics already present inthe smart battery. For example, in a system where the smart batteryindicates the desired charging voltage and charging current to the smartbattery charger 32, the smart battery charger 32 may not be required tomeasure or precisely control the voltage and current outputs. In such afeedback system, the smart battery can perform all of the measurementand control functions to cause the smart battery charger 32 to providethe desired voltage and current. The smart battery charger 32 is onlyrequired to respond monotonically to the signals from the smart battery34.

Smart battery charger 32 may be defined in three levels: Level 1, Level2 and Level 3. Each has a particular set of characteristics and minimumcommand set. At all levels, the smart battery charger 32 is able tocommunicate with the smart battery using the SMBus 38. The difference isthe ability of the smart battery charger 32 to provide charging servicesto the smart battery 34. Level 2 chargers support all Level 1 commands.Level 3 chargers support all Level 1 and Level 2 commands.

A Level 1 smart battery charger 32 operates with a fixed chargingalgorithm and only interprets the smart battery's 34 critical warningmessages that indicate that the battery should no longer be charged ordischarged. It is not able to adjust its output in response to requestsfrom the smart battery or the system host. The Level 1 charger istherefore not chemistry independent and is of limited utility inapplications where multiple chemistries are expected. The Level 1charger may use a smart battery's thermistor to determine if aNi-Cd/Ni-MH or some other type battery chemistry which tolerates aconstant current charge is present. When the thermistor is not presentor exhibits a very low value (e.g., less than 500 Ω), the Level 1charger will refuse to output any charge. This is a safety precautionthat may be supported by all levels of smart battery chargers.

A Level 2 smart battery charger 32 not only interprets the smartbattery's 34 critical warning messages, but is an SMBus slave devicethat responds to charging voltage and charging current messages sent toit by the smart battery 34 by dynamically adjusting its chargingoutputs. Smart battery 34 is in the best position to tell smart batterycharger 32 how it can best be charged. The charging algorithm in thebattery may simply request a charge condition once or may choose toperiodically adjust the smart battery charger's 32 output to meet itspresent needs. The smart battery 34 may also send a pattern of charginginformation for a portion of (e.g., burst or pulse) or a complete chargecycle to smart battery charger 32. The Level 2 smart battery charger 32is truly chemistry independent.

A Level 3 smart battery charger 32 not only interprets the smartbattery's 34 critical warning messages, but is a SMBus master device. Itmay poll the smart battery 34 to determine the charging voltage andcurrent the battery desires. The Level 3 charger 32 then dynamicallyadjusts its output to meet the battery's charging requirements. Thesmart battery 34 is in the best position to tell the smart batterycharger 32 how it wants to be charged. Using the charging algorithm inthe battery, the Level 3 charger may simply set a charge condition onceor may choose to periodically adjust the charger's 32 output to meet thechanging needs of the Smart Battery 34. A Level 3 smart battery chargeris free to implement an alternative specialized charging algorithm (e.g.a medical device may have a stricter temperature limit than the SmartBattery's self-contained charging algorithm, a Level 3 charger couldfactor in the battery's reported temperature along with the chargingcurrent and voltage into its charging algorithm). Like the Level 2charger, Level 3 smart battery charger is also chemistry independent. ALevel 3 smart battery charger may also interrogate the smart battery 34for other relevant data, such as time remaining to full charge, batterytemperature or other data used to control proper charging or dischargeconditioning.

Communication between the smart battery 34 and the smart battery charger32 may be initiated by the battery or the charger depending upon thespecific implementation, but the same information is transmitted fromthe battery to the charger, regardless of which device initiated thetransaction. For example, a Level 3 charger may poll the batteryperiodically to determine the appropriate charge voltage and current,while a Level 2 charger must wait for the battery to initiate the datatransmission. In both cases, data is supplied by the battery to thecharger. Communications between smart battery 34 and smart batterycharger 32 are performed: to allow the smart battery 34 to instruct thesmart battery charger 32 to set the appropriate charge current andcharge voltage, to allow access to the "correct" charge algorithm forthe battery, to allow smart batteries to be charged as rapidly and assafely as possible, and to allow new and different battery technologiesto be used.

Turning now to battery charging characteristics, FIG. 11A is a graphillustrating the -dV/dt (voltage decrease) at end-of-charge for typicalNi-Cd and Ni-MH batteries. FIG. 11B is an exemplary graph illustrating abattery's charging characteristic for temperatures of 0° C., 20° C., and45° C. The graph shows that higher temperature decreases the voltage atend-of-charge. FIG. 11C is a graph illustrating a typical battery'scharging characteristics for charging currents of 0.1 C, 0.3 C, and 1.0C. The graph shows that a higher charging current increases the chargingvoltage. Using such charging characteristics, the smart battery can tella smart battery charger the optimal charging current and chargingvoltage for charging under any present capacity and environmentalconditions of the battery.

FIG. 12 is a flowchart illustrating the present invention method forpredicting the recharge time of a battery. For example, the powermanagement system in a computer may provide the following chargingoptions to a user:

    ______________________________________                                        User Selects   System Uses a Charge Rate of:                                  ______________________________________                                        Quick Charge   1000 mA                                                        Medium Charge   300 mA                                                        Conserve Battery Life                                                                         100 mA                                                        Select a Charge Rate                                                                         <enter a charge rate>                                          ______________________________________                                    

These represent user-selectable recharge condition options available tothe user. However, what the user may really be interested in is whetherher battery can be recharged before a critical meeting in 45 minutes. Ifthe user selects the "Quick Charge" option the present inventionrecharge time prediction method may predict a recharge time of 30minutes based on present battery capacity. The user may also be informedthat a Quick Charge has a significantly larger impact on shortening thebattery's life than other options. Selecting the "Medium Charge" optionmay predict a recharge time of 60 minutes. Selecting the "ConserveBattery Life" option may predict a recharge time of 2 hours. If the"Select a Charge Rate" option is selected, the user can enter a customcharge rate. Alternatively, the user can select a custom charge time.Thus, predicted battery recharge time based on user-defined charge ratesallows the user to determine the charge rate option that best matcheshis present needs.

Turning to the present invention method for predicting the recharge timeof a battery, at step 140 a charge rate is selected. The charge rate maybe selected by a user, a power management system, or by other means.Alternatively, a default charge rate (such as the present charge rate)may be selected. The system host queries the battery for the predictedbattery recharge time based on either the present charge conditions orthe selected charge rate.

At step 142, the method determines the predicted battery recharge timeby: 1) measuring the battery's environmental conditions, such as batterytemperature, 2) determining present battery capacity, preferably by themethod of FIG. 6, and 3) determining the predicted recharge time of thebattery based on the measured environmental conditions, the presentbattery capacity, either the present charge conditions or the selectedcharge rate, and one or more characteristics of the battery. Forexample, the charging characteristics of FIG. 11A, FIG. 11B, and FIG.11C may be used.

At step 144, the battery indicates the predicted battery recharge timeto the system host via the SMBus.

Thus, a smart battery charger system including a smart battery chargerthat responds to charging instructions of a smart battery has beendescribed.

What is claimed is:
 1. A smart battery charger for charging a smartbattery, comprising:a nonvolatile memory that stores a charging currentvalue and a charging voltage value; a logic unit coupled to thenonvolatile memory, the logic unit programming the charging currentvalue into the nonvolatile memory in response to a set current valuecommand and programming the charging voltage value into the memory inresponse to a set voltage value command; and a charging unit coupled tothe nonvolatile memory, the charging unit generates a charging currentand a charging voltage according to the charging current value and thecharging voltage value, respectively.
 2. The smart battery charger ofclaim 1 further comprising a bidirectional communication circuit thatreceives the set current value command and the set voltage valuecommand.
 3. The smart battery charger of claim 1 wherein the chargingcurrent value and the charging voltage value are upper limits for thecharging current and the charging voltage, respectively.
 4. A smartbattery charger system comprising:(A) a smart battery including:(i) afirst nonvolatile memory fiat stores at least one chargingcharacteristic of the smart battery; and (ii) a first logic unit thatdetermines a desired charging current and a desired charging voltageaccording to at least one environmental condition of the battery and theat least one charging characteristic and writes the desired chargingcurrent and the desired charging voltage into the first nonvolatilememory; and (B) a smart battery charger coupled to the smart battery,the smart battery charger generates an actual charging current and anactual charging voltage in response to the desired charging current andthe desired charging voltage, respectively.
 5. The smart battery chargersystem of claim 4 wherein the at least one environmental conditionincludes a temperature of the smart battery.
 6. The smart batterycharger system of claim 4 wherein the at least one environmentalcondition includes at least one of temperature, humidity, and airpressure.
 7. The smart battery charger system of claim 4 wherein thesmart battery further includes:(iii) a monitoring circuit coupled to thefirst logic unit, the monitoring circuit measuring the at least oneenvironmental condition of the smart battery.
 8. The smart batterycharger system of claim 4 wherein the desired charging current and thedesired charging voltage are determined according to one or moreenvironmental conditions of the battery, the desired charging current,and the charging characteristics.
 9. The smart battery charger system ofclaim 4 wherein the smart battery further includessensor and feedbackcircuitry coupled to the first logic unit that measure the actualcharging current, the actual charging voltage, and the at least oneenvironmental condition of the battery; and wherein the first logic unitdetermines remaining run-time, recharge time, and charging conditionthat are destructive to the smart battery and sends an alarm signal tothe smart battery charger based on the actual charging current, actualcharging voltage, and the at least one environmental condition of thesmart battery.
 10. The smart battery charger system of claim 9 whereinthe smart battery charger removes the destructive charging conditions inresponse to the alarm signal.
 11. The smart battery charger of claim 4wherein the desired charging and the desired charging voltage are upperlimits for the actual charging current and the actual charging voltage,respectively.
 12. The smart battery charger according to claim 1,wherein the logic unit receives one of the set current value command andset voltage value command from a system host.
 13. The smart batterycharger according to claim 2, wherein the bi-directional communicationcircuit is a bus.
 14. The smart battery charger according to claim 13,wherein the logic unit receives at least one of the current valuecommand and the set voltage value command from a device coupled to thebi-directional communication circuit.
 15. The smart battery chargersystem according to claim 4, wherein the smart battery charger iscoupled to the smart battery through a bus.
 16. The smart batterycharger system according to claim 15, wherein the bus is further coupledto a system host and at least one input/output device.
 17. The smartbattery charger system according to claim 16, wherein the system host isone of a notebook computer, a video camera, and a cellular phone. 18.The smart battery charger system according to claim 4, wherein the smartbattery charger includes:a second nonvolatile memory that stores acharging current value and a charging voltage value; a second logic unitcoupled to the second nonvolatile memory, the second logic unitprogramming the charging current value into the second nonvolatilememory in response to a set current value command and programming thecharging voltage value into the second nonvolatile memory in response toa set voltage value command; and a charging unit coupled to the secondnonvolatile memory, the charging unit generates a charging current and acharging voltage according to the charging current value and thecharging voltage value, respectively.
 19. The smart battery chargersystem of claim 18 further comprising a bi-directional communicationcircuit that receives the set current value command and the set voltagevalue command.